In an exhaust gas turbocharger, the exhaust gases of an internal combustion engine can be used for compressing the combustion air which is fed to the engine. With precompressed or charged combustion air, the capacity, and therefore also the fuel mixture in the cylinders of the engine, can be increased and a power increase for the engine is gained. A known exhaust gas turbocharger includes a rotor with a compressor impeller, a turbine wheel and a connecting shaft, a bearing arrangement, housing sections, such as compressor housing or turbine housing which are fixed and charged with a mass flow, and a bearing housing which accommodates the bearing arrangement.
Because of the mostly high process pressures in the turbine-side and also compressor-side flow regions, the turbocharger shaft is sealed in relation to the inner plenum of the bearing housing by a suitable sealing method. The internal pressure in the plenum of the bearing housing can correspond to an atmospheric pressure of 1 bar. By contrast, the gas pressure in the flow region of the compressor side and turbine side depends upon the current operating point of the turbocharger and in most cases can lie above the plenum pressure of the bearing housing. In order to counteract pressure equalization, the section of the rotor which is supported in the bearing housing is therefore guided out of the bearing housing via two seals, of which one seals the bearing housing in the direction of the compressor and the other in the direction of the turbine. In certain cases a negative pressure in the compressor housing or in the turbine housing should be taken into consideration, for example, during partial load operation or during a shutdown period, when lubricating oil can find its way from the bearing housing into the turbine housing or compressor housing. In the compressor housing, penetrating lubricating oil could contaminate the charged compressor air and subsequently lead to unwanted emissions by combusting in the engine.
Exhaust gas turbochargers with sealing devices of this type are described in CH 673 052 A5 and in EP 0 834 645 A1. These devices can seal a bearing housing which holds lubricating oil, from which a rotor supported inside the casing of an exhaust gas turbocharger is guided into a compressor housing which is chargeable by a mass flow of the charger. The devices have a partition which separates an oil-collecting chamber, which is enclosed by a bearing housing of the turbocharger, and an impeller backspace of a compressor housing, from each other. In addition, the devices have a sealing disk which is fastened on a shaft of a turbocharger rotor and a collecting channel for lubricating oil which discharges from the bearing of the rotor into the oil-collecting chamber. The discharging lubricating oil can be thrown outwards by a rotating sealing disk, impinge upon the bearing-housing wall, run along the wall into the oil-collecting channel, flow via the channel downwards into an oil drain and from there flow back again into the oil circuit of the bearing lubricating system. A seal which is arranged between a rotor and a partition can ensure that different pressures in the spaces which are enclosed by the compressor housing and the bearing housing do not lead to unwanted compensating flows. The seal, as shown in CH 673 052 A5, can be constructed as a sealing ring and be arranged in a separating gap between the rotating sealing disk and the partition but as shown in EP 0 834 645 A1, can also be a labyrinth seal which is arranged in the impeller backspace between the impeller and the partition.
Further embodiments of sealing devices are also described in WO 2008/042698 A1. These sealing devices can have an oil-collecting channel which is formed in a fixed partition and arranged in an oil-collecting chamber. Lubricating oil which flows from a shaft bearing of an exhaust gas turbocharger via an axial bearing gap into the oil-collecting chamber can be thrown against the wall of the oil-collecting chamber, flow along the wall into the channel, and via the channel flow downwards into an oil drain. In the lower part of the channel, the oil can flow down on the right-hand and on the left-hand channel walls. Because the separating gap, which is provided between rotor and partition, leads into one of these two channel walls, at operating points with negative pressure on the compressor side that the separating gap is evacuated, despite seals being disposed in between, oil can find its way via these seals into the compressor of the turbocharger and as a result, into the intake air of an internal combustion engine.
U.S. Pat. No. 4,664,605 describes a further sealing device which can prevent penetration of lubricating oil from the shaft bearing of an exhaust gas turbocharger into the compressor. This sealing device has an oil-collecting chamber which by a shielding plate 15 is divided into two sub-chambers. The lubricating oil which discharges radially from an axial bearing of the turbocharger can be thrown outwards, impinge upon the shielding plate 15 of a first sub-chamber, is collected in a channel 45 which is formed in the plate 15 and via openings 57, 59 and a tongue 17A and is transported into an oil drain 27. The discharging lubricating oil can also find its way into a second sub-chamber 16 of the oil-collecting chamber. The oil can then be guided along a partition 10, which separates the sub-chamber 16 from an impeller backspace 1d of the compressor, downwards into the oil drain 27. In so doing, however, it can find its way into a separating gap which is arranged between a sealing disk 14, which is fastened and therefore rotates on the rotor 7 of the turbocharger, and the fixedly mounted partition 10. In the separating gap, there is a seal 11 which seals the impeller backspace 1d in relation to the sub-chamber 16 of the oil-collecting chamber but which during operation of the turbocharger can be impermissibly heavily loaded by lubricating oil which can penetrate from the sub-chamber 16 into the separating gap.
A device for addressing penetration of lubricating oil from the shaft bearing of an exhaust gas turbocharger into the compressor is disclosed in JP 07/217,441 A. This sealing device also has an oil-collecting chamber which is divided into two sub-chambers by a shielding plate. The lubricating oil which discharges radially from an axial bearing of the turbocharger can be thrown outwards, impinge upon a shielding plate 41 of a first sub-chamber and run down along the plate in a part 41e into a bearing-housing plenum and back again into an oil circuit of a bearing lubricating system. Through a gap in a part 41d, oil can find its way along a centrifugal disk 42 into a second chamber 40. The oil runs along a partition 30 downwards into a channel and further, in a part 30b, into the bearing-housing plenum. In this case, the channel is formed from a wall extension 30d of the partition and a rotating part of the flank 42 (FIG. 7). In the lower sector of the wall extension 30d, two drip edges 30e of a drip device for the oil are formed. In between them, however, in the upper sector, lies an axially extended gap which separates a rotor of the turbocharger from a fixed partition and which can be filled with oil. At operating points with negative pressure on a compressor side, despite installing a seal 35 in the separating gap, the separating gap can be evacuated and oil can find its way via the seal 35 into the compressor.